Capture Detection for Multi-Chamber Pacing

ABSTRACT

Multi-chamber pacing may result in capture of one chamber, capture of multiple chambers, fusion, or non-capture. Approaches for detecting various capture conditions during multi-chamber pacing are described. Pacing pulses are delivered to left and right heart chambers during a cardiac cycle. A cardiac electrogram signal is sensed following the delivery of the pacing pulses. Left chamber capture only, right chamber capture only, and bi-chamber capture may be distinguished based on characteristics of the cardiac electrogram signal. Multi-chamber capture detection may be implemented using detection windows having dimensions of time and amplitude. The detection windows are associated with expected features, such as expected signal peaks, under a particular capture condition. The cardiac electrogram signal features are compared to detection windows to determine the capture condition.

RELATED PATENT DOCUMENTS

This application is a continuation of U.S. patent application Ser. No.11/116,563 filed on Apr. 28, 2005, which is incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to cardiac devices and methods,and, more particularly, to cardiac devices and methods used in detectingcapture in multi-chamber pacing.

BACKGROUND OF THE INVENTION

When functioning normally, the heart produces rhythmic contractions andis capable of pumping blood throughout the body. The heart hasspecialized conduction pathways in both the atria and the ventriclesthat enable the rapid conduction of excitation impulses (i.e.depolarizations) from the SA node throughout the myocardium. Thesespecialized conduction pathways conduct the depolarizations from the SAnode to the atrial myocardium, to the atrioventricular node, and to theventricular myocardium to produce a coordinated contraction of bothatria and both ventricles.

The conduction pathways synchronize the contractions of the musclefibers of each chamber as well as the contraction of each atrium orventricle with the opposite atrium or ventricle. Without thesynchronization afforded by the normally functioning specializedconduction pathways, the heart's pumping efficiency is greatlydiminished. Patients who exhibit pathology of these conduction pathwayscan suffer compromised cardiac output.

Cardiac rhythm management devices have been developed that providepacing stimulation to one or more heart chambers in an attempt toimprove the rhythm and coordination of atrial and/or ventricularcontractions. Cardiac rhythm management devices typically includecircuitry to sense signals from the heart and a pulse generator forproviding electrical stimulation to the heart. Leads extending into thepatient's heart chamber and/or into veins of the heart are coupled toelectrodes that sense the heart's electrical signals and for deliveringstimulation to the heart in accordance with various therapies fortreating cardiac arrhythmias.

Pacemakers are cardiac rhythm management devices that deliver a seriesof low energy pace pulses timed to assist the heart in producing acontractile rhythm that maintains cardiac pumping efficiency. Pacepulses may be intermittent or continuous, depending on the needs of thepatient. There exist a number of categories of pacemaker devices, withvarious modes for sensing and pacing one or more heart chambers.

A pace pulse must exceed a minimum energy value, or capture threshold,to produce a contraction. It is desirable for a pace pulse to havesufficient energy to stimulate capture of the heart chamber withoutexpending energy significantly in excess of the capture threshold. Thus,accurate determination of the capture threshold is required forefficient pace energy management. If the pace pulse energy is too low,the pace pulses may not reliably produce a contractile response in theheart chamber and may result in ineffective pacing. If the pace pulseenergy is too high, the patient may experience discomfort and thebattery life of the device will be shorter.

Detecting if a pacing pulse “captures” the heart and produces acontraction allows the pacemaker to adjust the energy level of pacepulses to correspond to the optimum energy expenditure that reliablyproduces capture. Further, capture detection allows the pacemaker toinitiate a back-up pulse at a higher energy level whenever a pace pulsedoes not produce a contraction.

When a pace pulse produces a contraction in the heart chamber, theelectrical cardiac signal preceding the contraction is denoted thecaptured response. The captured response typically includes anelectrical signal, denoted the evoked response signal, associated withthe heart contraction, along with a superimposed signal associated withresidual post pace polarization at the electrode-tissue interface. Themagnitude of the residual post pace polarization signal, or pacingartifact, may be affected by a variety of factors including leadpolarization, after-potential from the pace pulse, lead impedance,patient impedance, pace pulse width, and pace pulse amplitude, forexample. The evoked response may be affected by interaction withintrinsic heart activity and resulting in a fusion or pseudofusionresponse.

Multi-chamber pacemakers may include electrodes positioned to contactcardiac tissue within or adjacent to both the left and the rightventricles for pacing both the left and right ventricles. This type ofdevice allows bi-ventricular pacing therapy to be applied, for example,to coordinate ventricular contractions when a patient suffers fromcongestive heart failure (CHF). Furthermore, multi-chamber pacemakersmay include electrodes positioned to contact tissue within or adjacentto both the left and the right atria to enable bi-atrial pacing.

It is desirable to determine if pacing pulses delivered to multipleheart chambers produce a captured response in one, both, or none of thepaced chambers. The present invention provides methods and systems usedfor enhancing the discrimination of the cardiac response tomulti-chamber pacing and provides various advantages over the prior art.

SUMMARY OF THE INVENTION

The present invention involves approaches for detecting various captureconditions during multi-chamber pacing. One embodiment of the inventioninvolves a method for detection various capture conditions. Pacingpulses are delivered to left and right heart chambers during a cardiaccycle. A cardiac electrogram signal is sensed following the delivery ofthe pacing pulses. The method includes distinguishing between leftchamber capture only, right chamber capture only, and bi-chamber capturebased on characteristics of the cardiac electrogram signal.

According to one aspect, the pacing pulses are delivered to left andright ventricles. The method includes distinguishing between leftventricular capture only, right ventricular capture only, andbi-ventricular capture.

The cardiac electrogram signal may be sensed, for example, using anelectrode positioned in, on or within a vein of the right heart chamber,using an electrode positioned in, on, or within a vein of the left heartchamber or using both left heart chamber and right heart chamberelectrodes.

In one implementation, each of the templates, comprising detectionwindows having dimensions of time and amplitude, are associated withleft chamber capture, right chamber capture, or bi-chamber capture. Thecardiac electrogram signal is compared to one or more of the templatesto determine the type of capture condition. The detection windows areassociated with an expected feature, e.g., peaks, of the cardiacelectrogram under a particular capture condition.

Another embodiment of the invention involves a cardiac device. Thecardiac device includes a sensing channel configured to sense a cardiacelectrogram signal following delivery of pacing pulses delivered to leftand right heart chambers, respectively, during a cardiac cycle. Aprocessor coupled to the sensing circuitry, the processor configured todistinguish between left chamber capture only, right chamber captureonly, and bi-chamber capture based on characteristics of the cardiacsignal.

The above summary of the present invention is not intended to describeeach embodiment or every implementation of the present invention.Advantages and attainments, together with a more complete understandingof the invention, will become apparent and appreciated by referring tothe following detailed description and claims taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart illustrating a method of capture detection inaccordance with embodiments of the invention;

FIG. 2 is a partial view of one embodiment of an implantable medicaldevice suitable for implementing multi-chamber capture detection inaccordance with embodiments of the invention;

FIG. 3 is a block diagram of an implantable medical device suitable forimplementing multi-chamber capture detection in accordance withembodiments of the invention.

FIGS. 4A and 4B provide a flowchart illustrating a method ofbi-ventricular capture detection in accordance with embodiments of theinvention;

FIG. 5 is a graph illustrating detection windows used for detectingbi-ventricular capture and right ventricle only capture in accordancewith embodiments of the invention;

FIG. 6 is a graph illustrating detection windows used for detectingbi-ventricular capture and left ventricle only capture in accordancewith embodiments of the invention;

FIG. 7 is a flowchart illustrating a method of performing amulti-chamber capture threshold test in accordance with embodiments ofthe invention;

FIG. 8 is a flowchart illustrating a method of confirming the capturecondition in accordance with embodiments of the invention; and

FIGS. 9A and 9B are flowcharts illustrating methods of selecting anelectrode for capture sensing in accordance with embodiments of theinvention.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail below. It is to be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the invention isintended to cover all modifications, equivalents, and alternativesfalling within the scope of the invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

In the following description of the illustrated embodiments, referencesare made to the accompanying drawings forming a part hereof, and inwhich are shown by way of illustration, various embodiments by which theinvention may be practiced. It is to be understood that otherembodiments may be utilized, and structural and functional changes maybe made without departing from the scope of the present invention.

A pacemaker or other cardiac rhythm management device may determinewhether an applied electrical pacing stimulus captures a heart chamber.The systems and methods described herein involve the use of features ofa cardiac electrogram to discriminate between various types of cardiacresponses to multi-chamber pacing. The approaches of the presentinvention provide for enhanced capture threshold testing and/or beat tobeat automatic capture verification for multi-chamber pacing, forexample.

Several functions of cardiac devices rely on the heart responseconsistency. For example, automatic capture threshold testing and/orautomatic capture verification algorithms may rely on templates of theheart's response as the basis for determining whether a future pacingstimulus produces a particular type of response. Templatesrepresentative of various types of cardiac responses may comprise one ormore detection windows. The detection windows are compared to a cardiacsignal following delivery of multi-chamber pacing. In multi-chamberpacing, pacing pulses delivered to two opposite, i.e., left and right,heart chambers during a cardiac cycle. In accordance with embodiments ofthe invention, the cardiac signal following pacing is analyzed todiscriminate, for example between left heart chamber capture, rightheart chamber capture, multi-chamber capture, fusion and non-capture.

FIG. 1 is a flowchart illustrating a method of multi-chamber capturedetection in accordance with embodiments of the invention. Pacing pulsesare delivered 110 to left and right heart chambers during a cardiaccycle. For example, a pacing pulse may be delivered to the leftventricle (LV) and to the right ventricle (RV). The pacing pulses may bedelivered over separate pacing channels and may be deliveredsubstantially simultaneously or may be separated in time by aninterventricular delay (IVD). The cardiac signal following delivery ofthe pacing pulses is sensed 120. The cardiac signal may be sensed, forexample, using an evoked response sensing channel that is configured fordetection of the cardiac response to the multi-chamber pacing. Thecardiac response to the multi-chamber pacing is determined based oncharacteristics of the sensed cardiac signal. Capture of the leftchamber only, right chamber only, multi-chamber capture, fusion ornon-capture may be discriminated 130.

The embodiments of the present system illustrated herein are generallydescribed as being implemented in a patient implantable medical device(PIMD) such as a pacemaker/defibrillator (PD) that may operate innumerous pacing modes known in the art. Various types of multiplechamber implantable cardiac pacemaker/defibrillators are known in theart and may be used in connection with cardiac devices and methods thatprovide multi-chamber capture detection in accordance with theapproaches of the present invention. The methods of the presentinvention may be implemented in a variety of implantable orpatient-external cardiac rhythm management devices, includingmulti-chamber pacemakers, defibrillators, cardioverters, bi-ventricularpacemakers, cardiac resynchronizers, and cardiac monitoring systems, forexample.

A device suitable for implementing the capture detection methods of thepresent invention may include stimulation circuitry from deliveringstimulation pulses to the heart and includes sensing circuitrycomprising electrodes electrically coupled to the heart. Leads from thesensing and/or stimulation circuitry are coupled to electrodespositioned within heart chambers, positioned within veins of the heart,and/or positioned on the heart. The electrodes sense the heart'selectrical signals, which are denoted cardiac electrogram signals. Eachlead may include multiple electrodes, and each electrode may be used tosense a separate electrogram signal for capture detection.

Although the present system is described in conjunction with animplantable cardiac pacemaker/defibrillator having amicroprocessor-based architecture, it will be understood that theimplantable pacemaker/defibrillator (or other device) may be implementedusing any logic-based circuit architecture, if desired.

Referring now to FIG. 2 of the drawings, there is shown a partial viewof a cardiac rhythm management device that may be used to implementmulti-chamber capture detection in accordance with the presentinvention. The cardiac rhythm management device in FIG. 2 includes apacemaker/defibrillator 800 electrically and physically coupled to alead system 802. The housing and/or header of thepacemaker/defibrillator 800 may incorporate one or more electrodes 908,909 used to provide electrical stimulation energy to the heart and tosense cardiac electrical activity. The pacemaker/defibrillator 800 mayutilize all or a portion of the pacemaker/defibrillator housing as a canelectrode 909. The pacemaker/defibrillator 800 may include anindifferent electrode 908 positioned, for example, on the header or thehousing of the pacemaker/defibrillator 800. If thepacemaker/defibrillator 800 includes both a can electrode 909 and anindifferent electrode 908, the electrodes 908, 909 typically areelectrically isolated from each other.

The lead system 802 is used to detect electric cardiac signals producedby the heart 801 and to provide electrical energy to the heart 801 undercertain predetermined conditions to treat cardiac arrhythmias. The leadsystem 802 may include one or more electrodes used for pacing, sensing,and/or defibrillation. In the embodiment shown in FIG. 2, the leadsystem 802 includes an intracardiac right ventricular (RV) lead system804, an intracardiac right atrial (RA) lead system 805, an intracardiacleft ventricular (LV) lead system 806, and an extracardiac left atrial(LA) lead system 808. The lead system 802 of FIG. 2 illustrates oneembodiment that may be used in connection with the multi-chamber capturedetection methodologies described herein. Other leads and/or electrodesmay additionally or alternatively be used.

The lead system 802 may include intracardiac leads 804, 805, 806implanted in a human body with portions of the intracardiac leads 804,805, 806 inserted into a heart 801. The intracardiac leads 804, 805, 806include various electrodes positionable within the heart for sensingelectrical activity of the heart and for delivering electricalstimulation energy to the heart, for example, pacing pulses and/ordefibrillation shocks to treat various arrhythmias of the heart.

As illustrated in FIG. 2, the lead system 802 may include one or moreextracardiac leads 808 having electrodes, e.g., epicardial electrodes,positioned at locations outside the heart for sensing and pacing one ormore heart chambers.

The right ventricular lead system 804 illustrated in FIG. 2 includes anSVC-coil 816, an RV-coil 814, an RV-ring electrode 811, and an RV-tipelectrode 812. The right ventricular lead system 804 extends through theright atrium 820 and into the right ventricle 819. In particular, theRV-tip electrode 812, RV-ring electrode 811, and RV-coil electrode 814are positioned at appropriate locations within the right ventricle 819for sensing and delivering electrical stimulation pulses to the heart801. The SVC-coil 816 is positioned at an appropriate location withinthe right atrium chamber 820 of the heart 801 or a major vein leading tothe right atrial chamber 820 of the heart 801.

In one configuration, the RV-tip electrode 812 referenced to the canelectrode 909 may be used to implement unipolar pacing and/or sensing inthe right ventricle 819. Bipolar pacing and/or sensing in the rightventricle may be implemented using the RV-tip 812 and RV-ring 811electrodes. In yet another configuration, the RV-ring 811 electrode mayoptionally be omitted, and bipolar pacing and/or sensing may beaccomplished using the RV-tip electrode 812 and the RV-coil 814, forexample. The RV-coil 814 and the SVC-coil 816 are defibrillationelectrodes.

The left ventricular lead 806 includes an LV distal electrode 813 and anLV proximal electrode 817 located at appropriate locations in or aboutthe left ventricle 824 for pacing and/or sensing the left ventricle 824.The left ventricular lead 806 may be guided into the right atrium 820 ofthe heart via the superior vena cava. From the right atrium 820, theleft ventricular lead 806 may be deployed into the coronary sinusostium, the opening of the coronary sinus 850. The lead 806 may beguided through the coronary sinus 850 to a coronary vein of the leftventricle 824. This vein is used as an access pathway for leads to reachthe surfaces of the left ventricle 824 which are not directly accessiblefrom the right side of the heart. Lead placement for the leftventricular lead 806 may be achieved via subclavian vein access and apreformed guiding catheter for insertion of the LV electrodes 813, 817adjacent to the left ventricle.

Unipolar pacing and/or sensing in the left ventricle may be implemented,for example, using the LV distal electrode referenced to the canelectrode 909. The LV distal electrode 813 and the LV proximal electrode817 may be used together as bipolar sense and/or pace electrodes for theleft ventricle. The left ventricular lead 806 and the right ventricularlead 804, in conjunction with the pacemaker/defibrillator 800, may beused to provide cardiac resynchronization therapy such that theventricles of the heart are paced substantially simultaneously, or inphased sequence, to provide enhanced cardiac pumping efficiency forpatients suffering from chronic heart failure.

The right atrial lead 805 includes a RA-tip electrode 856 and an RA-ringelectrode 854 positioned at appropriate locations in the right atrium820 for sensing and pacing the right atrium 820. In one configuration,the RA-tip 856 referenced to the can electrode 909, for example, may beused to provide unipolar pacing and/or sensing in the right atrium 820.In another configuration, the RA-tip electrode 856 and the RA-ringelectrode 854 may be used to provide bipolar pacing and/or sensing.

FIG. 2 illustrates one embodiment of a left atrial lead system 808. Inthis example, the left atrial lead 808 is implemented as an extracardiaclead with LA distal 818 and LA proximal 815 electrodes positioned atappropriate locations outside the heart 801 for sensing and pacing theleft atrium 822. Unipolar pacing and/or sensing of the left atrium maybe accomplished, for example, using the LA distal electrode 818 to thecan 909 pacing vector. The LA proximal 815 and LA distal 818 electrodesmay be used together to implement bipolar pacing and/or sensing of theleft atrium 822. The right atrial lead 805 and the left atrial lead 808may be used in conjunction with the pacemaker/defibrillator 800 toprovide bi-atrial pacing.

Referring now to FIG. 3, there is shown a block diagram of a cardiacpacemaker/defibrillator 900 suitable for implementing multi-chambercapture detection methods of the present invention. FIG. 3 shows acardiac pacemaker/defibrillator 900 divided into functional blocks. Itis understood by those skilled in the art that there exist many possibleconfigurations in which these functional blocks can be arranged. Theexample depicted in FIG. 3 is one possible functional arrangement. Otherarrangements are also possible. For example, more, fewer or differentfunctional blocks may be used to describe a cardiacpacemaker/defibrillator suitable for implementing the methodologies formulti-chamber capture detection in accordance with the presentinvention. In addition, although the cardiac pacemaker/defibrillator 900depicted in FIG. 3 contemplates the use of a programmablemicroprocessor-based logic circuit, other circuit implementations may beutilized.

The cardiac pacemaker/defibrillator 900 depicted in FIG. 3 includescircuitry for receiving cardiac signals from a heart and deliveringelectrical stimulation energy to the heart in the form of pacing pulsesor defibrillation shocks. In one embodiment, the circuitry of thecardiac pacemaker/defibrillator 900 is encased and hermetically sealedin a housing 901 suitable for implanting in a human body. Power to thecardiac pacemaker/defibrillator 900 is supplied by an electrochemicalbattery 980. A connector block (not shown) is attached to the housing901 of the cardiac pacemaker/defibrillator 900 to allow for the physicaland electrical attachment of the lead system conductors to the circuitryof the cardiac pacemaker/defibrillator 900.

The cardiac pacemaker/defibrillator 900 may be a programmablemicroprocessor-based system, including a control system 920 and a memory970. The memory 970 may store parameters for various pacing,defibrillation, and sensing modes, along with other parameters. Further,the memory 970 may store data indicative of cardiac signals received byother components of the cardiac pacemaker/defibrillator 900. The memory970 may be used, for example, for storing historical cardiac electrogramand therapy data. The historical data storage may include, for example,data obtained from long-term patient monitoring used for trending and/orother diagnostic purposes. Historical data, as well as otherinformation, may be transmitted to an external programmer unit 990 asneeded or desired.

The control system 920 and memory 970 may cooperate with othercomponents of the cardiac pacemaker/defibrillator 900 to control theoperations of the cardiac pacemaker/defibrillator 900. The controlsystem 920 depicted in FIG. 3 incorporates detection window circuitry926 configured to provide multi-chamber capture detection as describedherein.

The control system 920 further includes a cardiac responseclassification processor 925 that works in conjunction with thedetection window circuitry 926. The cardiac response classificationprocessor 925 performs the function of analyzing the location of cardiacsignal features with respect to one or more detection windows todetermine the cardiac response to pacing.

The control system 920 may include additional functional componentsincluding a pacemaker control circuit 922, an arrhythmia detector 921,along with other components for controlling the operations of thecardiac pacemaker/defibrillator 900.

Telemetry circuitry 960 may be implemented to provide communicationsbetween the cardiac pacemaker/defibrillator 900 and an externalprogrammer unit 990. In one embodiment, the telemetry circuitry 960 andthe programmer unit 990 communicate using a wire loop antenna and aradio frequency telemetric link, as is known in the art, to receive andtransmit signals and data between the programmer unit 990 and thetelemetry circuitry 960. In this manner, programming commands and otherinformation may be transferred to the control system 920 of the cardiacpacemaker/defibrillator 900 from the programmer unit 990 during andafter implant. In addition, stored cardiac data pertaining to capturethreshold, capture detection and/or cardiac response classification, forexample, along with other data, may be transferred to the programmerunit 990 from the cardiac pacemaker/defibrillator 900.

The telemetry circuitry 960 may provide for communication between thecardiac pacemaker/defibrillator 900 and an advanced patient management(APM) system. The advanced patient management system allows physiciansor other personnel to remotely and automatically monitor cardiac and/orother patient conditions. In one example, a cardiacpacemaker/defibrillator, or other device, may be equipped with varioustelecommunications and information technologies that enable real-timedata collection, diagnosis, and treatment of the patient. Variousembodiments described herein may be used in connection with advancedpatient management.

Methods, structures, and/or techniques described herein, which may beadapted to provide for remote patient/device monitoring, diagnosis,therapy, or other APM related methodologies, may incorporate features ofone or more of the following references: U.S. Pat. Nos. 6,221,011;6,270,457; 6,277,072; 6,280,380; 6,312,378; 6,336,903; 6,358,203;6,368,284; 6,398,728; and 6,440,066, which are hereby incorporatedherein by reference.

In the embodiment of the cardiac pacemaker/defibrillator 900 illustratedin FIG. 3, electrodes RA-tip 856, RA-ring 854, RV-tip 812, RV-ring 811,RV-coil 814, SVC-coil 816, LV distal electrode 813, LV proximalelectrode 817, LA distal electrode 818, LA proximal electrode 815,indifferent electrode 908, and can electrode 909 are coupled through aswitch matrix 910 to sensing circuits 931-937.

A right atrial sensing circuit 931 serves to detect and amplifyelectrical signals from the right atrium of the heart. Bipolar sensingin the right atrium may be implemented, for example, by sensing voltagesdeveloped between the RA-tip 856 and the RA-ring 854. Unipolar sensingmay be implemented, for example, by sensing voltages developed betweenthe RA-tip 856 and the can electrode 909. Outputs from the right atrialsensing circuit are coupled to the control system 920.

A right ventricular sensing circuit 932 serves to detect and amplifyelectrical signals from the right ventricle of the heart. The rightventricular sensing circuit 932 may include, for example, a rightventricular rate channel 933 and a right ventricular shock channel 934.Right ventricular cardiac signals sensed through use of the RV-tip 812electrode are right ventricular near-field signals and are denoted RVrate channel signals. A bipolar RV rate channel signal may be sensed asa voltage developed between the RV-tip 812 and the RV-ring 811.Alternatively, bipolar sensing in the right ventricle may be implementedusing the RV-tip electrode 812 and the RV-coil 814. Unipolar ratechannel sensing in the right ventricle may be implemented, for example,by sensing voltages developed between the RV-tip 812 and the canelectrode 909.

Right ventricular cardiac signals sensed through use of thedefibrillation electrodes are far-field signals, also referred to as RVmorphology or RV shock channel signals. More particularly, a rightventricular shock channel signal may be detected as a voltage developedbetween the RV-coil 814 and the SVC-coil 816. A right ventricular shockchannel signal may also be detected as a voltage developed between theRV-coil 814 and the can electrode 909. In another configuration the canelectrode 909 and the SVC-coil electrode 816 may be electrically shortedand a RV shock channel signal may be detected as the voltage developedbetween the RV-coil 814 and the can electrode 909/SVC-coil 816combination.

Left atrial cardiac signals may be sensed through the use of one or moreleft atrial electrodes 815, 818, which may be configured as epicardialelectrodes. A left atrial sensing circuit 935 serves to detect andamplify electrical signals from the left atrium of the heart. Bipolarsensing and/or pacing in the left atrium may be implemented, forexample, using the LA distal electrode 818 and the LA proximal electrode815. Unipolar sensing and/or pacing of the left atrium may beaccomplished, for example, using the LA distal electrode 818 to canvector 909 or the LA proximal electrode 815 to can vector 909.

A left ventricular sensing circuit 936 serves to detect and amplifyelectrical signals from the left ventricle of the heart. Bipolar sensingin the left ventricle may be implemented, for example, by sensingvoltages developed between the LV distal electrode 813 and the LVproximal electrode 817. Unipolar sensing may be implemented, forexample, by sensing voltages developed between the LV distal electrode813 or the LV proximal electrode 817 and the can electrode 909.

Optionally, an LV coil electrode (not shown) may be inserted into thepatient's cardiac vasculature, e.g., the coronary sinus, adjacent theleft heart. Signals detected using combinations of the LV electrodes,813, 817, LV coil electrode (not shown), and/or can electrodes 909 maybe sensed and amplified by the left ventricular sensing circuitry 936.The output of the left ventricular sensing circuit 936 is coupled to thecontrol system 920.

The outputs of the switching matrix 910 may be operated to coupleselected combinations of electrodes 811, 812, 813, 814, 815, 816, 817,818, 856, 854 to an evoked response sensing circuit 937. The evokedresponse sensing circuit 937 serves to sense and amplify signalsdeveloped using various combinations of electrodes for discrimination ofvarious cardiac responses to pacing in accordance with embodiments ofthe invention. The cardiac response classification processor 925 maycooperate with detection window circuitry 926 to analyze the output ofthe evoked response sensing circuit 937 for implementation ofmulti-chamber cardiac pacing response classification.

Various combinations of pacing and sensing electrodes may be utilized inconnection with pacing and sensing the cardiac signal following the pacepulses to determine the cardiac response to the pacing pulse. Thepacemaker control circuit 922, in combination with pacing circuitry forthe left atrium, right atrium, left ventricle, and right ventricle 941,942, 943, 944, may be implemented to selectively generate and deliverpacing pulses to the heart using various electrode combinations. Thepacing electrode combinations may be used to effect bipolar or unipolarpacing pulses to a heart chamber using one of the pacing vectors asdescribed above.

In some implementations, the cardiac pacemaker/defibrillator 900 mayinclude a sensor 961 that is used to sense the patient's hemodynamicneed. In one implementation, the sensor may comprise, for example, anaccelerometer configured to sense patient activity. In anotherimplementation, the sensor may comprise an impedance sensor configuredto sense patient respiration. The pacing output of the cardiacpacemaker/defibrillator may be adjusted based on the sensor output.

The electrical signal following the delivery of the pacing pulses may besensed through various sensing vectors coupled through the switch matrix910 to the evoked response sensing circuit 937 and/or other sensingcircuits and used to classify the cardiac response to pacing. Thecardiac response may be classified as one of left chamber capture only,right chamber capture only, multi-chamber capture, fusion andnon-capture, for example.

Subcutaneous electrodes may provide additional sensing vectors useablefor cardiac response classification. In one implementation, cardiacrhythm management system may involve a hybrid system including anintracardiac device configured to pace the heart and an extracardiacdevice, e.g., a subcutaneous defibrillator, configured to performfunctions other than pacing. The extracardiac device may be employed todetect and classify cardiac response to pacing based on signals sensedusing subcutaneous electrode arrays. The extracardiac and intracardiacdevices may operate cooperatively with communication between the devicesoccurring over a wireless link, for example. Examples of subcutaneouselectrode systems and devices are described in commonly owned U.S.Publication Nos. 2004/0230229 and 2004/0230230, which are herebyincorporated herein by reference in their respective entireties.

FIG. 4 is a flowchart illustrating a multi-chamber capture method inaccordance with the present invention as applied to a bi-ventricularpacing embodiment. Detection windows are provided 402, each detectionwindow corresponding to an expected feature of the cardiac signal underconditions of LV capture, RV capture or bi-ventricular capture. Thedetection windows may be provided based on clinical data taken from anumber of patients or may be formed based on data taken from thepatient.

In one implementation, detection windows associated with a particularcapture condition may be formed by measuring a number of cardiac signalsof the patient under the particular capture condition, extracting one ormore features from each of the cardiac signals, clustering the features,and determining detection window boundaries based on the clusteredfeatures. In one implementation, the features extracted and clusteredcomprise positive and negative cardiac signal peaks. Forming detectionwindows based on clustering is described in commonly owned U.S.Publication No. 2006/0247707, which is hereby incorporated herein byreference. The one or more detection windows used for detecting theparticular capture condition form a detection template. Detectionwindows and templates comprising one or more detection windows for eachcapture condition (LV capture, RV capture, and bi-ventricular capture)may be formed using the clustering approach or other methods.

In some cases, pacing the ventricles based on tracked atrial events isused to more closely mimic the patient's natural rhythm. During acardiac cycle, an atrial pacing pulse is delivered to the atrium oratrial activity is sensed 404. An atrioventricular (AV) delay isinitiated 406 relative to the sensed or paced atrial event. The AV delaymay have a predetermined, programmable, or automatically adjustableduration.

Maintaining consistent bi-ventricular pacing enhances cardiacresynchronization. The AV delay may be set to a relatively shortduration relative to the patient's AV conduction time to promotebi-ventricular pacing.

The first and second ventricles may be paced substantiallysimultaneously or in phased sequence. In one implementation, a firstventricle (left or right) is paced 408 relative to the AV delay and thesecond ventricle (right or left) is paced 410 relative aninterventricular (IV) delay. The interventricular delay may be a fixed,programmable, or automatically adjustable duration.

The sensing channel used for capture detection, e.g., evoked responsechannel, is blanked 412 after the ventricular paces. For example, theevoked response channel may be blanked during the interventricular delayand for about 0 milliseconds to about 40 milliseconds after the lastventricular pace. After blanking, the cardiac signal is sensed 414. Thecardiac signal comprises a cardiac electrogram signal that may be sensedusing one or more electrodes positioned within one or more heartchambers and/or within one or more veins of the heart. In thisimplementation, the cardiac electrogram signal may be sensed using anelectrode positioned in the right ventricle (RV tip electrode, RV ringelectrode or RV coil electrode), an electrode positioned within a veinof the left ventricle (LV distal electrode or LV proximal electrode),and/or electrodes positioned in the right ventricle and the leftventricular vein, for example. The cardiac signal is compared to anactivity detection threshold (ADT) which comprises positive and negativethresholds. If the cardiac signal does not exceed 416 the ADT in eitherthe positive or negative direction, then the cardiac response isdetermined 418 to be a non-captured response. If non-capture isdetected, 418 a back up pace may be delivered 420 to one or bothventricles.

If the cardiac signal exceeds 416 the ADT, the cardiac signal morphologyis compared to the expected morphology associated with various captureconditions. Cardiac signal features are extracted and compared todetection windows comprising a template associated with a particulartype of capture condition. Cardiac signal features may be compared 422to one or more of a template associated with bi-ventricular capture, atemplate associated with LV capture and a template associated with RVcapture.

In one implementation, the extracted features of the cardiac signal maycomprise positive and negative peaks. The amplitude and timing of thecardiac signal peaks may be compared to expected peak amplitudes andpeak times associated with capture conditions LV capture, RV capture,and/or bi-ventricular capture.

If the cardiac signal peaks fall within one or more detection windowsassociated with LV capture, then the capture condition is determined 426to be LV capture. If the cardiac signal peaks fall within one or moredetection windows associated with RV capture, then the capture conditionis determined 424 to be RV capture. If the cardiac signal peaks fallwithin on or more detection windows associated with bi-ventricularcapture, then the capture condition is determined 428 to bebi-ventricular capture. If the cardiac signal peaks do not fall withinany of the detection windows, or if the cardiac signal peaks fall withinmultiple detection windows representing different capture conditions,then the capture condition may be determined to be fusion.

If the features of the cardiac signal are consistent with a particularcapture template, then the particular capture template may be updated430 using the features. Methods and systems for updating cardiac pacingresponse templates are described in commonly owned U.S. Publication No.2006/0247696, which is hereby incorporated herein by reference.

FIG. 5 provides a composite graph of signals representative ofbi-ventricular capture 510 and of signals representative of RV captureonly (LV non-capture) 520. These signals follow pacing pulses deliveredto the right and left ventricles. A signal similar to the bi-ventricularcapture signals 510 is produced when the pacing pulses capture bothventricles. A signal similar to the RV capture signals 520 is producedwhen the pacing pulse delivered to the right ventricle captures theright ventricle and the pacing pulse delivered to the left ventricledoes not capture the left ventricle.

Both the bi-ventricular capture signals 510 and the RV capture signals520 have an initial peak followed by a peak of opposite polarity.However, the signals 510, 520 differ in morphology. As can be seen fromFIG. 5, the morphology of the signals 520 associated with RV onlycapture have slightly wider peak widths and the peaks are delayed intime when compared to the signals 510 associated with bi-ventricularcapture.

The morphological differences between signals associated withbi-ventricular capture 510 and signals associated with RV capture 520can be utilized to discriminate between bi-ventricular capture and RVcapture. FIG. 5 illustrates detection windows 512, 514 522, 524 that maybe used to discriminate between bi-ventricular capture and RV capture.

First 512 and second 514 bi-ventricular detection windows are used todetect bi-ventricular capture. If the positive peak of a cardiac signalfalls within the first bi-ventricular detection window 512 and thenegative peak of the cardiac signal falls within the secondbi-ventricular detection window 514, then the system determines thatboth the left and the right ventricles were captured by the pacingpulses.

If the positive peak of the cardiac signal falls in the first RV capturedetection window 522 and the negative peak of the cardiac signal fallsin the second RV capture detection window 524, then the systemdetermines that the pacing pulse delivered to the right ventriclecaptured the right ventricle and the pacing pulse delivered to the leftventricle did not capture the left ventricle. If the positive ornegative value of the cardiac signal does not exceed the ADT 505, thenneither ventricle was captured. If the cardiac signal peaks do not fallwithin any of the detection windows, or if the cardiac signal peaks fallwithin multiple detection windows representing the two captureconditions, then the capture condition may be determined to be fusion.

FIG. 6 provides a composite graph of signals representative ofbi-ventricular capture 610 and of signals representative of LV captureonly (RV non-capture) 620. These signals follow pacing pulses deliveredto the right and left ventricles. A signal similar to the bi-ventricularcapture signals 610 is produced when the pacing pulses capture bothventricles. A signal similar to the LV capture signals 620 is producedwhen the pacing pulse delivered to the left ventricle captures the leftventricle and the pacing pulse delivered to the right ventricle does notcapture the right ventricle.

As can be seen from FIG. 6, the signals associated with LV capture 620have peaks that are inverted and delayed in time when compared to thesignals associated with bi-ventricular capture 610. The morphologicaldifferences between signals associated with bi-ventricular capture andsignals associated with LV capture can be utilized to discriminatebetween bi-ventricular capture and LV capture. FIG. 6 illustratesdetection windows 612, 614, 622 that may be used to discriminate betweenbi-ventricular capture and LV capture.

First 612 and second 614 bi-ventricular detection windows are used todetect bi-ventricular capture. If the positive peak of a cardiac signalfalls within the first bi-ventricular detection window 612 and thenegative peak of the cardiac signal falls within the secondbi-ventricular detection window 614, then the system determines thatboth the left and the right ventricles were captured by the pacingpulses.

If the positive peak of the cardiac signal falls in the LV capturedetection window 622 then the system determines that the pacing pulsedelivered to the left ventricle captured the left ventricle and thepacing pulse delivered to the right ventricle did not capture the rightventricle. If the amplitude of the cardiac signal does not exceed theADT 605, in either the positive or negative direction, then neitherventricle was captured. If the cardiac signal peaks do not fall withinany of the detection windows, or if the cardiac signal peaks fall withinmultiple detection windows representing the two capture conditions, thenthe capture condition may be determined to be fusion.

By way of example, the processes of the present invention may be used toenhance capture threshold testing to determine a suitable energy forpacing. Determination of a suitable pacing energy may be implemented,for example, by an automatic capture threshold testing procedureexecuted by an implantable pacemaker/defibrillator or other cardiacrhythm management device. Additionally, automatic capture verificationmay be used, for example, to monitor capture on a beat-by-beat basis.Automatic capture verification may be used to control back up pacingwhen a pace pulse delivered to the heart fails to evoke a capturedresponse. These and other applications may be enhanced by themulti-chamber capture approaches of the present invention.

Those skilled in the art will appreciate that reference to a capturethreshold testing procedure indicates a method of determining thecapture threshold in one or more of the left atrium, the right atrium,both the left atrium and the right atrium, the left ventricle, the rightventricle, and/or both the left ventricle and the right ventricle. Insuch a procedure, the pacemaker, automatically or upon command,initiates a search for the capture threshold of the selected heartchamber or chambers. The capture threshold is defined as the lowestpacing energy that consistently produces a contraction of the heartchamber.

In one example of an automatic capture threshold procedure, thepacemaker delivers a sequence of pacing pulses to the heart chamber orchambers and detects the cardiac responses to the pace pulses. Theenergy of the pacing pulses may be decreased in discrete steps until apredetermined number of loss-of-capture events occur. After thepredetermined number of loss-of-capture events occur, the pacemaker mayincrease the stimulation energy in discrete steps until a predeterminednumber of capture events occur to confirm the capture threshold. Acapture threshold test may be performed using the multi-chamber capturedetection approaches of the present invention.

Other procedures for implementing capture threshold testing may beutilized. In one example, the pacing energy may be initially set to zeroor a relatively low pacing energy and then increased in discrete stepsuntil capture is detected. In another example, the pacing energy may beadjusted according to a binomial search pattern.

Automatic capture threshold determination is distinguishable fromautomatic capture verification, a procedure that may occur on abeat-by-beat basis during pacing. Automatic capture verificationverifies that a delivered pace pulse results in a captured response.When a captured response is not detected following a pace pulse, thepacemaker may deliver a back up safety pace to ensure consistent pacing.The back up pace may be delivered, for example, about 90-110 ms afterthe initial pace pulse. If a predetermined number of pace pulsesdelivered during normal pacing do not produce a captured response, thepacemaker may initiate a capture threshold test to determine the capturethreshold. Automatic capture verification and back up pacing may beimplemented using the multi-chamber capture detection processes of thepresent invention.

FIG. 7 illustrates an automatic capture threshold testing procedure formulti-chamber pacing using multi-chamber capture detection in accordancewith approaches of the invention. The pacing energy of first and secondheart chambers is initialized 710 to a value exceeding the capturethreshold, such as a maximum pacing value. Blocks 715-730 illustrate amethod of incrementally decreasing 715 the pacing energy of the firstchamber until loss of capture (LOC) occurs 730. After each incrementalreduction 715 in pacing energy, the first and second chambers are paced720. The cardiac signal following the pacing energy is sensed 725 andcompared to one or more detection windows associated with expectedcharacteristics of multi-chamber capture and/or second chamber onlycapture and/or first chamber only capture. If the signal characteristicsare consistent with second chamber only capture, then loss of capture ofthe first chamber is detected 730. The first chamber energy value isstored 735 as the first chamber capture threshold.

The pacing energy of the first chamber is reinitialized 740 to a valueexceeding the capture threshold. Blocks 745-755 illustrate a method ofincrementally decreasing 745 the pacing energy of the second chamberuntil loss of capture (LOC) occurs 755. After each incremental reduction745 in pacing energy, the first and second chambers are paced 750. Thecardiac signal following the pacing energy is sensed 752 and compared toone or more detection windows associated with expected characteristicsof multi-chamber capture and/or second chamber only capture and/or firstchamber only capture. If the signal characteristics are consistent withfirst chamber only capture, then loss of capture of the second chamberis detected 755. The second chamber energy value is stored 760 as thesecond chamber capture threshold.

In some embodiments, a first electrogram signal may be used to determinethe capture condition and one or more additional electrogram signals maybe used to confirm or increase a level of confidence in the capturedetermination. In some implementations, the first electrogram signal maybe sensed using an electrode electrically coupled to a first heartchamber and an additional electrogram signal may be sensed using anelectrode electrically coupled to a second heart chamber. In someimplementations, the first and additional electrogram signals may besensed using electrodes electrically coupled to the same chamber.

The processor may evaluate the first and additional cardiac electrogramsignals to distinguish capture conditions in various combinations. Forexample, the processor may evaluate the first signal to discriminatebetween a first two of right chamber capture only, left chamber captureonly, and multi-chamber capture to determine the capture condition. Theprocessor may use an additional signal to distinguish between a secondtwo of right chamber capture only, left chamber capture only, andmulti-chamber capture to confirm the capture condition. Distinguishingbetween other combinations of capture conditions including left chambercapture only, right chamber capture only, multi-chamber capture,non-capture, and fusion for capture confirmation is possible.

A process of using an additional electrocardiogram signal for confirmingcapture determination is illustrated by the flowchart of FIG. 8. Pacingpulses are delivered 1010 to left and right heart chambers during acardiac cycle. A first electrogram signal is sensed 1020, for example,using an electrode associated with a first heart chamber. A secondelectrocardiogram is sensed 1030, for example, using an electrodeassociated with a second heart chamber. The capture condition isdetermined 1040 using the first signal. The second signal is used toconfirm 1050 or increase confidence in the capture conditiondetermination.

In some embodiments, a selected electrode may be used to determine thecapture condition. The selection may be based on parameters of thesignal produced using the electrode, including, for example, signalintegrity (signal to noise ratio), suitability for capture detection,sensitivity to a particular capture condition, e.g., LV capture orbi-ventricular capture, over sense condition, lead impedance outside apredetermined range, capture amplitude voltage outside a predeterminedrange, intrinsic amplitude outside a predetermined range, detection ofunintended non-cardiac stimulation, failure to detect an expected eventand/or other parameters of the signal. FIGS. 9A and 9B are flowchartsillustrating electrode selection processes in accordance withembodiments of the invention.

FIGS. 9A and 9B illustrate methods of selecting capture sensingelectrodes for use in automatic capture threshold testing and/or beat tobeat automatic capture verification. The process illustrated in FIG. 9Amay be particularly suited, for example, for use in connection with anautomatic capture threshold test. Prior to beginning the test, thesignals produced by available electrode combinations are evaluated 1101with respect to signal to noise ratio and/or other parameters associatedwith capture detection suitability as described above. An electrodecombination is selected 1105 for capture detection during the test.Pacing pulses are delivered 1110 to left and right heart chambers. Thecardiac signal is sensed 1115 using the selected electrode combination.The capture condition is determined 1120 based on characteristics of thesensed signal.

The capture determination process illustrated by the flowchart of FIG.9B may be used, for example, to select between available electrodecombinations in beat to beat automatic capture verification, and/orother capture detection processes. The illustrated process allows thepacemaker to switch between capture sensing electrodes if the signalfrom a particular electrode combination becomes noisy or producesunreliable capture results. An initial electrode combination is selected1125 for capture sensing. Pacing pulses are delivered 1130 to the leftand right heart chambers. A cardiac electrogram signal is sensed 1135using the selected electrode combination. If the signal is suitable 1140for capture detection, e.g., not noisy, minimum signal level, etc., thenthe capture condition is determined 1150 based on the signalcharacteristics. If the signal is unsuitable 1140 for capture detection,particularly if the signal is persistently unsuitable, then the systemmay select 1145 a different electrode combination. Methods and systemsfor selective use of various electrode combinations to improve capturedetection and other pacemaker/defibrillator functions, aspects of whichmay be utilized in connection with the present invention, are describedin commonly owned U.S. Pat. No. 6,493,586 which is incorporated hereinby reference.

The components, functionality, and structural configurations depictedherein are intended to provide an understanding of various features andcombination of features that may be incorporated in an implantablepacemaker/defibrillator. It is understood that a wide variety of cardiacmonitoring and/or stimulation device configurations are contemplated,ranging from relatively sophisticated to relatively simple designs. Assuch, particular cardiac device configurations may include particularfeatures as described herein, while other such device configurations mayexclude particular features described herein.

Various modifications and additions can be made to the preferredembodiments discussed hereinabove without departing from the scope ofthe present invention. Accordingly, the scope of the present inventionshould not be limited by the particular embodiments described above, butshould be defined only by the claims set forth below and equivalentsthereof.

1. A method of operating a cardiac rhythm management device in a patientto classify a cardiac response to multi-chamber pacing, comprising:delivering a first pacing pulse to a left heart chamber during a cardiaccycle; delivering a second pacing pulse to a right heart chamber duringthe cardiac cycle; sensing a cardiac electrogram signal following thefirst and second pacing pulses; determining at least whether (a) a firstsignal feature of the cardiac signal is disposed within a firstdetection window, and (b) a second signal feature of the cardiac signalis disposed within a second detection window, at least one of the firstand second detection windows being finitely bounded in both time andamplitude; and classifying the cardiac response to the first and secondpacing pulses as one of bi-chamber capture and a single chamber capturebased on the determination of (a) and (b).
 2. The method of claim 1,wherein the first signal feature comprises a first peak and the secondsignal feature comprises a second peak of the cardiac signal.
 3. Themethod of claim 1, wherein both the first and second detection windowsare finitely bounded in both time and amplitude.
 4. The method of claim3, wherein the first detection window covers a first amplitude range andthe second detection window covers a second amplitude range opposite inpolarity to the first amplitude range.
 5. The method of claim 3, whereinthe first detection window covers a first amplitude range and the seconddetection window covers a second amplitude range of the same polarity asthe first amplitude range.
 6. The method of claim 1, wherein the singlechamber capture refers to capture of a specific one of the left andright heart chambers.
 7. The method of claim 1, wherein the first andsecond detection windows are non-overlapping.
 8. The method of claim 1,wherein the first detection window is associated with bi-chamber captureand the second detection window is associated with a specific singlechamber capture.
 9. The method of claim 1, wherein the first and seconddetection windows are both associated with bi-chamber capture.
 10. Themethod of claim 1, wherein the determining step also determines whether(c) a third signal feature of the cardiac signal is disposed within athird detection window, and the classifying step is based also on thedetermination of (c).
 11. The method of claim 1, wherein the first andsecond pacing pulses are delivered substantially simultaneously.
 12. Themethod of claim 1, wherein the left heart chamber is a left ventricleand the right heart chamber is a right ventricle.
 13. An implantablesystem for classifying a cardiac response to multi-chamber pacingpulses, comprising: a pulse delivery system configured to deliver afirst pacing pulse to a left heart chamber during a cardiac cycle and asecond pacing pulse to a right heart chamber during the cardiac cycle; asensor system configured to sense a cardiac electrogram signal followingthe first and second pacing pulses; and a processor coupled to thesensor system, the processor configured to determine whether (a) a firstsignal feature of the cardiac signal is disposed within a firstdetection window, and (b) a second signal feature of the cardiac signalis disposed within a second detection window, the processor furtherbeing configured to classify the cardiac response to the first andsecond pacing pulses as one of bi-chamber capture and a single chambercapture based on the determination of (a) and (b); wherein at least oneof the first and second detection windows is finitely bounded in bothtime and amplitude.
 14. The system of claim 13, wherein the first signalfeature comprises a first peak and the second signal feature comprises asecond peak of the cardiac signal.
 15. The system of claim 13, whereinboth the first and second detection windows are finitely bounded in bothtime and amplitude.
 16. The system of claim 15, wherein the firstdetection window covers a first amplitude range and the second detectionwindow covers a second amplitude range opposite in polarity to the firstamplitude range.
 17. The system of claim 15, wherein the first detectionwindow covers a first amplitude range and the second detection windowcovers a second amplitude range of the same polarity as the firstamplitude range.
 18. The system of claim 13, wherein the single chambercapture refers to capture of a specific one of the left and right heartchambers.
 19. The system of claim 13, wherein the first and seconddetection windows are non-overlapping.
 20. The system of claim 13,wherein the first detection window is associated with bi-chamber captureand the second detection window is associated with a specific singlechamber capture.
 21. The system of claim 13, wherein the first andsecond detection windows are both associated with bi-chamber capture.22. The system of claim 13, wherein the processor is also configured todetermine whether (c) a third signal feature of the cardiac signal isdisposed within a third detection window, and the processor isconfigured to classify the cardiac response based on the determinationof (a), (b), and (c).
 23. The system of claim 13, wherein the pulsedelivery system is configured to deliver the first and second pacingpulses substantially simultaneously.
 24. The system of claim 13, whereinthe left heart chamber is a left ventricle and the right heart chamberis a right ventricle.